1. Field of the Invention
The present invention relates to a projector which projects and displays an image on a screen.
2. Description of the Related Prior Art
Heretofore, it has been a common practice to correct a keystone caused by a tilt projection of an image only by a vertical processing, and the projector used to be installed at a position squarely facing with a screen as far as a horizontal direction is concerned.
In recent years, however, with the advent of a correction function for the horizontal keystone, it became possible to perform the corrections vertically, horizontally and diagonally.
Among those corrections, the correction for the screen still depends on a manual correction. If the correction is only for vertical or horizontal keystone, it can be easily performed manually, but the manual correction is difficult for the diagonal distortion.
There are systems proposed (for example, the inventions disclosed in Japanese Unexamined Patent Application Publication No. 2001-169211 and Japanese Unexamined Patent Application Publication No. 2001-083949), in which the correction function of this type can be made possible by providing an image taken from an observing point different from the projector.
Further, there is available a projector which detects a distance from a projection lens to the screen and calculates an angle of inclination from this detection result, thereby automatically making it possible to provide the distortion correction (for example, inventions disclosed in Japanese Patent Laid-Open No. 4-355740, Japanese Unexamined Patent Application Publication No. 2000-81593; and Japanese Unexamined Patent Application Publication No. 2000-122617).
However, the above-described prior art comprises a range finder independently from the primary function of the projector, and does not take steps and the like to use a projection image. Besides, to measure the distance of a plurality of positions, a plurality of finders is required.
Moreover, it is not described on a relative positional relationship with an image to be projected. With respect to the projection image, since it widely changes the position and size of its image plane depending on a status of the projection lens, it is unknown whether or not a correction adequate to the projected image is really made by simply just measuring the positional relationship between the projector and the screen.
Furthermore, with respect to a position to be measured as well, due to an installation error of the finder and a variation of a mechanical positional relationship between the projection lens and a display device, it is not possible to show a correct position.
In addition, in the case where a frame and the like exist just outside the screen and protrudes endways or the screen itself is set far back and the like, a measured position of the finder and a screen position do not always match.